Orbital-Tailored Pt Sites via Atomic-Level Carrier Pre-Design for Enhanced Photocatalytic Hydrogen Evolution

Modulating the coordination geometry of single atoms (SAs) is crucial for overcoming the limitations in catalytic activity. This study aims to construct a clear relationship between the coordination geometry of Pt SAs and their catalytic activity to guide the synthesis of targeted high-activity SA catalysts. An interesting atomic-level predesign strategy for SA carriers is proposed, enabling precise atomic regulation of N_2c coordination sites. Seven distinct SA carriers were synthesized: pristine CN, N_v-CN (1, 2, 3) with N_2c vacancies and O_d-CN (1, 2, 3), in which N_2c sites are substituted by oxygen doping, thereby achieving the controlled synthesis of four Pt coordination geometries: Pt-N₄ in pristine CN, Pt-N₂Cl₄ (reconstructed to Pt-N₂) in N_v-CN, and Pt-N₃O in O_d-CN. Among these, O_d-CN-Pt exhibited exceptional photocatalytic hydrogen evolution performance (66.4 mmol g^-1 h^-1), which is 3.75 and 2.7 times higher than that of CN-Pt and N_v-CN-Pt, respectively. By combining <i>in-situ</i> KPFM-SPV, X-ray photoelectron spectroscopy, femtosecond transient absorption, and density functional theory calculations, a volcano-type relationship model was established between activity and three descriptors Bader charge, Pt 5d intensity, and Δ<i>E</i> (from PDOS to the Fermi level)─to elucidate the correlation between the coordination geometry and catalytic activity of SA-based catalysts. Such a descriptor may guide the predesign of high-performance SA catalysts.